نتایج جستجو برای: permian system
تعداد نتایج: 2233955 فیلتر نتایج به سال:
During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore develop...
Rhythmic sandstone-mudstone-coal succession of the Barakar Formation (early Permian) manifests a transition from lower braided-fluvial to upper tide-wave influenced, estuarine setting. Monospecific assemblage of marine trace fossil Chondrites isp. in contemporaneous claystone beds in the upper Barakar succession from two Gondwana basins (namely, the Raniganj Basin and the Talchir Basin) in east...
Long-term extensive mining of Zn-Pb ores in the Olkusz area resulted in significant changes of water table levels and chemical composition of water in all aquifers in this area. Within the Permian aquifer, hydrochemical type of water evolved in two general stages. Short-term effect was freshening in the zones of contact with overlying the Triassic limestones and dolomites. Long-term effect was ...
The end-Permian mass extinction, ∼252 million years ago, is notable for a complex recovery period of ∼5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constr...
The supercontinent Pangea dominated our planet from the Permian into the Jurassic. Paleomagnetic reconstructions have been used to estimate the latitudinal position of Pangea during this 100-million-year period. Atmospheric circulation, recorded by eolian sandstones in the southwestern United States, shows a broad sweep of northeasterly winds over their northernmost extent, curving to become no...
S U M M A R Y The Upper Carboniferous-Lower Triassic Pyongan Supergroup is exposed in an E-W trending syncline comprising the Samcheok Coalfield in eastern South Korea; it borders the southern margin of a NE-SW trending (Okcheon) zone of Upper Jurassic-Lower Cretaceous deformation (Daebo Orogeny). Although a Recent field overprint widely recorded in Korean rocks is represented here, an ancient ...
The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (δ18Op)...
The origin of Hymenoptera remains controversial. Currently accepted hypotheses consider Hymenoptera as the first side branch of Holometabola or sister-group to Mecopteroidea. In contrast, fossils confirm the idea of Martynov that Hymenoptera are related to Megaloptera and Raphidioptera. Hymenoptera have descended along with Raphidioptera from the earliest Megaloptera, the Permian Parasialidae. ...
The identification of the factors triggering continental environmental changes at Permian–Triassic transition is general interest as they allow a better understanding most controversial mass extinction Phanerozoic. This study investigates response to external forcings on successions south-east-margin Central European Basin System in Germany. Studies from this area are scarce, and its evolution ...
Abstract Previous studies on multiple sulfur isotopes ( 32 S, 33 and 34 S) in sedimentary pyrite at the end‐Permian suggested a shoaling of anoxic/sulfidic deep‐water contributing to extinction. This scenario is based an assumption that cycle was largely controlled by benthos activity, though stratigraphic correlation between records ichnofabrics sediments has not yet been examined. We report i...
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